1. Field of the Invention
The present invention relates to a developing apparatus that uses one-component toner, and more particularly to a developing apparatus for an image forming device, such as an electrophotographic copier.
2. Description of the Related Art
Numerous developing apparatuses that use one-component toner, such as an electrophotographic copier, perform development by forming toner used as a developing material into a uniform thin layer, by electrically charging the toner as necessary, and by attaching the charged toner to an electrostatic latent image on an image carrier.
The development method specifically described below is well known. In this method, toner is first supplied to a rotating cylindrical toner carrier, and a layer thickness controlling member extending in parallel with the toner carrier is made contact with the outer peripheral surface of the toner carrier to which the toner has been supplied, whereby the toner on the toner carrier is formed into a uniform thin layer. At the same time, the toner is electrically charged as necessary for development by friction charging, charge implantation or the like. After this, the charged toner layer is transferred to the contact portion wherein the image carrier makes contact with the toner carrier as the toner carrier rotates. The toner on the toner carrier is attached to an electrostatic latent image on an image carrier.
In the case of the above-mentioned development method, a method of controlling the thickness of the toner layer is carried out frequently in order to obtain excellent image quality. In this method, the surface or the edges of the layer thickness controlling member having the shape of a thin plate formed of a metal member, a high molecular resin member or a lamination of a metal member and a high molecular resin member are made contact with the toner carrier in order to control the thickness of the toner layer.
In this case, toner is not consumed in the vicinity of both end portions of the toner carrier corresponding to the non-image area of the electrostatic latent image. Furthermore, toner is moved to both end portions of the toner carrier by the dispersion action as the toner carrier rotates. Toner is thus oversupplied, resulting in toner scattering and leakage. This causes problems of contaminating the inside of the device, increasing the consumption of toner and the like.
The related art in accordance with Japanese Examined Patent Publication JP-B2 4-62391 (1992) discloses a method of preventing toner from moving to both end portions of the toner carrier, thereby preventing toner from scattering. The developing apparatus in accordance with this method is provided with elastic sealing members for covering both side portions of the end portion of the layer thickness controlling member formed of an elastic material in its longitudinal direction from the back side of its contact surface making contact with the toner carrier. Alternatively, the developing apparatus is provided with elastic sealing members for pressurizing both side portions in the longitudinal direction of the layer thickness controlling member from the back side of its contact surface making contact with the toner carrier inward in the radial direction of the toner carrier.
In the developing apparatus in accordance with the related art disclosed in JP-B2 4-62391 or the like, sealing member are provided on the surface of the layer thickness controlling member making contact with the toner carrier, on the rear surface or on both end side surfaces of the layer thickness controlling member in order to prevent toner leakage. However, slight gaps are apt to occur at both side end portions of the layer thickness controlling member and at the contact portion wherein the layer thickness controlling member makes contact with the toner carrier because of steps caused by the thickness of the layer thickness controlling member. This results in toner scattering and leakage, and causes problems of staining images, contaminating the inside of the device, increasing toner consumption and the like.
If the sealing pressure of the sealing members is raised in order to prevent improper sealing due to the gap at the contact portion wherein the toner carrier makes contact with the layer thickness controlling member, the contact pressure force exerted from the layer thickness controlling member to the toner carrier in the radial direction of the toner carrier increases. This increase of the contact pressure force prevents normal operation of the layer thickness controlling member, and disturbs the formation of the toner layer near both end portions of the layer thickness controlling member, wherein the sealing members are disposed. As a result, image quality may apt to lower at both end portions of an image region, and improper sealing may be apt to occur because of sliding abrasion between the toner carrier and the sealing members or between the toner carrier and the layer thickness controlling member. It is thus very difficult for the above-mentioned developing apparatus to prevent toner scattering and leakage.
An object of the invention is to provide a developing apparatus capable of supplying a uniform thin layer of toner and capable of preventing toner scattering and leakage.
The invention provides a developing apparatus which performs development by supplying a thin toner layer to an electrostatic latent image on an image carrier, comprising a cylindrical toner carrier for transferring supplied toner to a development position by rotation of the toner carrier, supply means for supplying toner to an outer peripheral surface of the toner carrier, a layer thickness controlling member for controlling thickness of the supplied toner to within a predetermined value while making slide contact with the outer peripheral surface of the toner carrier, and sealing means for holding the layer thickness controlling member and preventing toner leakage,
wherein the layer thickness controlling member is formed of an elastic plate extending in parallel with the toner carrier, and has a bent portion which is convex toward the toner carrier and makes elastic contact with the outer peripheral surface of the toner carrier over a nearly entire length thereof, one end of the layer thickness controlling member in a width direction thereof with respect to the bent portion outwardly extending in a radial direction of the toner carrier, a portion on the other side of the layer thickness controlling member in the width direction thereof extending in a peripheral direction of the toner carrier toward a downstream side of the rotation direction of the toner carrier, and
the sealing means consisting of an upstream side sealing member which makes contact with the one end of the layer thickness controlling member from an upstream side of the rotation direction of the toner carrier and a downstream side sealing member which makes contact with the one end of the layer thickness controlling member from a downstream side of the rotation direction of the toner carrier, the one end of the layer thickness controlling member being caught between the upstream side sealing member and the downstream side sealing member so that the layer thickness controlling member is held to be elastically displaceable in the radial direction of the toner carrier.
In accordance with the invention, since the convex bent portion of the layer thickness controlling member makes elastic contact with the outer surface of the toner carrier, no step is formed by the thickness of the layer thickness controlling member unlike the related art. As a result, toner leakage can be prevented, and the thickness of the toner layer formed on the toner carrier can be made uniform.
In addition, since the one end of the layer thickness controlling member extending outward in the radial direction of the toner carrier is caught between the upstream side and downstream side sealing members, it is possible to reduce the contact pressure force exerted by the sealing members from the layer thickness controlling member to the toner carrier in the radial direction of the toner carrier. As a result, the sealing members can securely perform sealing without deterioration with a lapse of time without interfering with the movement of the layer thickness controlling member.
In accordance with the invention, between the upstream side sealing member and the downstream side sealing member is caught the one end of the layer thickness controlling member extending in the radial direction of the toner carrier thereby to hold the layer thickness controlling member so that the layer thickness controlling member can be elastically displaced elastically in the radial direction of the toner carrier as described above. The layer thickness controlling member can thus make elastic contact with the toner carrier, whereby it is possible to prevent any adverse effects on the layer thickness controlling member due to the pressure contact forces of the sealing members. The developing apparatus in accordance with the invention can therefore perform uniform toner layer formation, and can securely prevent toner leakage. As a result, in the developing apparatus, it is possible to prevent deterioration in image quality due to a nonuniform toner concentration, a change in concentration, fogging and stains, and it is also possible to prevent contamination inside the device due to toner scattering. Excellent images can thus be formed stably.
Furthermore, in the invention it is preferable that a main component of a pressure contact force exerted from the upstream side sealing member to the layer thickness controlling member is in parallel with the peripheral direction of the toner carrier.
In accordance with the invention, since the main component of the pressure contact force exerted from the upstream side sealing member to the layer thickness controlling member is in parallel with the peripheral direction of the toner carrier, it is possible to prevent the pressure contact force of the sealing members from increasing the pressure contact force of the layer thickness controlling member to the toner carrier. As a result, the developing apparatus in accordance with the invention can attain stable layer thickness control operation and can securely prevent toner leakage simultaneously.
Furthermore, in accordance with the invention, since the main component of the pressure contact force exerted from the upstream side sealing member to the layer thickness controlling member is in parallel with the peripheral direction of the toner carrier, the component of the pressure contact force in the radial direction of the toner carrier is almost negligible. It is thus possible to prevent the toner layer formation by the sealing members from being adversely affected.
Furthermore, in the invention it is preferable that the sealing means is disposed at both ends of the layer thickness controlling member in a longitudinal direction thereof and the upstream side sealing member has a side sealing member which makes contact with the toner carrier.
In accordance with the invention, the side sealing member which makes contact with the toner carrier is provided. It is thus possible to securely prevent toner leakage from the upstream side to the downstream side of the rotation direction of the toner carrier and toner leakage at both ends in the longitudinal direction of the layer thickness controlling member.
Furthermore, in accordance with the invention, since the side sealing member is provided at both ends of the layer thickness controlling member in the longitudinal direction thereof and makes contact with the toner carrier, the layer thickness controlling member can be held by the side sealing member, and toner leakage can be prevented from both ends of the layer thickness controlling member.
Furthermore, in the invention it is preferable that the side sealing member has a fur-planted cloth at a contact portion thereof which makes contact with the toner carrier.
In accordance with the invention, since the side sealing member has the fur-planted cloth at its contact portion which makes contact with the toner carrier, the side sealing member can prevent any sliding friction load between the side sealing member and the toner carrier.
Furthermore, in accordance with the invention, since the side sealing member has the fur-planted cloth at the contact portion making contact with the toner carrier, the side sealing member can prevent any sliding friction load between the side sealing member and the toner carrier. In addition, the side sealing member can securely prevent toner leakage at the contact portion wherein the layer thickness controlling member makes contact with the toner carrier without causing sliding abrasion and breakage. As a result, the side sealing member can securely perform stable sealing for a long time.
Furthermore, in the invention it is preferable that a fur-planting direction of the fur-planted cloth is a forward direction wherein an end of the fur tilts to the downstream side of the rotation direction of the toner carrier.
In accordance with the invention, since the fur-planting direction of the fur-planted cloth is the forward direction not opposite to the rotation direction of the toner carrier, it is possible to reduce the sliding friction resistance between the planted fur and the toner carrier.
Furthermore, in accordance with the invention, since the fur-planting direction of the fur-planted cloth is the forward direction wherein the end of the fur tilts to the downstream side of the rotation direction of the toner carrier, it is possible to reduce the friction resistance between the planted fur and the toner carrier.
Furthermore, in the invention it is preferable that the fur of the fur-planted cloth has such a length that the end of the fur reaches the contact portion wherein a toner carrier side surface of the convex bent portion of the layer thickness controlling member which is bent at a predetermined radius of curvature, makes contact with the outer peripheral surface of the toner carrier.
In accordance with the invention, the end of the fur of the side sealing member can be inserted securely into the contact portion wherein the layer thickness controlling member makes contact with the toner carrier. It is therefore possible to securely prevent toner leakage at the contact portion wherein the layer thickness controlling member makes contact with the toner carrier.
Furthermore, in accordance with the invention, since the fur of the fur-planted cloth has such a length that the end of the fur reaches the contact portion wherein the layer thickness controlling member makes contact with the toner carrier, the end of the planted fur can be securely inserted into the contact portion, and the reliability of the sealing can be improved.
Furthermore, in the invention it is preferable that the upstream side sealing member has a central sealing member for holding the layer thickness controlling member over a nearly entire length of the layer thickness controlling member in a longitudinal direction thereof.
In accordance with the invention, since the central sealing member is provided, it is possible to securely prevent toner leakage from the upstream side to the downstream side of the rotation direction of the toner carrier over the entire length of the layer thickness controlling member in the longitudinal direction without interfering with the movement of the layer thickness controlling member.
Furthermore, in accordance with the invention, the central sealing member for holding the layer thickness controlling member over the nearly entire length in the longitudinal direction can prevent toner leakage from the upstream side to the downstream side of the rotation direction of the toner carrier, and can securely seal toner over the entire length in the longitudinal direction.
Furthermore, in the invention it is preferable that the central sealing member does not make contact with the toner carrier.
In accordance with the invention, since the central sealing member does not make contact with the toner carrier, the central sealing member does not cause any adverse effects on the rotation of the toner carrier, and can securely prevent toner leakage from the upstream side to the downstream side of the rotation direction of the toner carrier.
Furthermore, in accordance with the invention, since the central sealing member does not make contact with the toner carrier, it is possible to prevent any sliding load to the toner carrier from increasing.
Furthermore, in the invention it is preferable that the central sealing member makes contact with the toner carrier at least in an effective region of an image.
In accordance with the invention, since the central sealing member makes pressure contact with the toner carrier in the image region, the toner supplied to the contact portion wherein the layer thickness controlling member makes contact with the toner carrier can be pre-charged with the result of enhancing uniformity of charging of a toner layer.
Furthermore, in accordance with the invention, since the central sealing member makes contact with the toner carrier via the toner layer in the image region, coagulated toner lumps are loosened. In addition, the toner is pre-charged and subjected to other processing. As a result, the toner layer can have higher uniformity, stability and reliability.
Furthermore, in the invention it is preferable that the upstream side sealing member is formed of a soft foam material having independent bubbles.
In accordance with the invention, since the upstream side sealing member is formed of a soft foam material, the upstream side sealing member can securely prevent toner leakage at a low sealing pressure contact force, and can prevent interference with the movement of the layer thickness controlling member.
Furthermore, in accordance with the invention, since the upstream side sealing member is formed of a soft foam material, it is possible to reduce the pressure contact force to the layer thickness controlling member or the toner carrier. In addition, since the soft foam material for the upstream side sealing member is a foam material having independent bubbles, it is possible to prevent toner from leaking through pores in the foam material.
Furthermore, in the invention it is preferable that the downstream side sealing member is bonded to a wall surface of a frame of a developing bath for accommodating toner.
In accordance with the invention, since the downstream side sealing member is bonded to the developing bath frame, it is possible to reduce the pressure contact force of the downstream side sealing member.
Furthermore, in accordance with the invention, since the downstream side sealing member is bonded to the wall surface of the developing bath frame, the assembly of the developing bath can be made more easily, and the sealing can have higher reliability.
Furthermore, in the invention it is preferable that the downstream side sealing member is bonded to the layer thickness controlling member.
In accordance with the invention, since the downstream side sealing member is bonded to the layer thickness controlling member, it is possible to reduce the pressure contact force of the downstream side sealing member.
Furthermore, in accordance with the invention, since the downstream side sealing member is bonded to the layer thickness controlling member, the sealing can have higher reliability. In addition, it is possible to use a sealing member having the same shape as that of the space defined by the developing bath frame and the layer thickness controlling member. The downstream side sealing member can therefore prevent toner leakage without affecting the pressure contact force exerted from the layer thickness controlling member to the toner carrier.
Furthermore, in the invention it is preferable that the downstream side sealing member is positioned inside both ends in a longitudinal direction of the layer thickness controlling member and do not make contact with the toner carrier.
In accordance with the invention, since the downstream sealing member does not make contact with the toner carrier, it is possible to prevent any sliding load from being applied to the toner carrier. As a result, it is possible to prevent the downstream side sealing member and the toner carrier from undergoing sliding abrasion.
Furthermore, in accordance with the invention, the downstream side sealing member can perform sealing without making contact with the toner carrier. As a result, it is possible to prevent any sliding load occurring between the downstream side sealing member and the toner carrier. It is thus possible to prevent deterioration due to abrasion and change with time associated with sliding.
Furthermore, in the invention it is preferable that a main component of a pressure contact force exerted from the downstream side sealing member to the layer thickness controlling member is in parallel with the peripheral direction of the toner carrier.
In accordance with the invention, since the main component of the pressure contact force exerted from the downstream side sealing member to the layer thickness controlling member is in parallel with the peripheral direction of the toner carrier, it is possible to prevent the pressure contact force generated by the elasticity of the downstream side sealing member from increasing the pressure contact force of the layer thickness controlling member to the toner carrier. As a result, the developing apparatus in accordance with the invention can attain stable layer thickness control operation and can securely prevent toner leakage simultaneously.
Furthermore, in accordance with the invention, since the direction of the pressure contact force exerted from the downstream side sealing member is in parallel with the peripheral direction of the toner carrier, the component of the pressure contact force exerted from the downstream side sealing member in the layer thickness control direction can be eliminated. It is thus possible to prevent the toner layer formation by the downstream side sealing member from being adversely affected.
Furthermore, in the invention it is preferable that the downstream side sealing member is formed of a soft foam material having independent bubbles.
In accordance with the invention, since the downstream side sealing member is formed of a soft foam material, the downstream side sealing member can securely prevent toner leakage at a low sealing pressure contact force, and can prevent interference with the movement of the layer thickness controlling member.
Furthermore, in accordance with the invention, since the downstream side sealing member is formed of a soft foam material, it is possible to reduce the pressure contact force of the downstream side sealing member. In addition, since the soft foam material for the downstream side sealing member is a foam material having independent bubbles, it is possible to prevent toner from leaking through the pores in the foam material.
Furthermore, in the invention it is preferable that the downstream side sealing member is formed of a soft foam material having a hardness of 250N or less in accordance with JIS K6401.
In accordance with the invention, the downstream side sealing member can securely prevent toner leakage at a low sealing pressure contact force, and can prevent interference with the movement of the layer thickness controlling member.
Furthermore, in accordance with the invention, since the downstream side sealing member is formed of a foam material having a hardness of 250N or less in accordance with JIS K6401, the downstream side sealing member can securely prevent toner leakage without interfering with the movement of the layer thickness controlling member, and can form a uniform toner layer stably.